Voice communication devices often employ a vocoder to synthesize and/or compress speech into an encoded voice signal. For example, the speech of a user talking on a cellular telephone can be received, digitized and compressed by a vocoder to generate an encoded voice signal. A voice communications session can be established between the user and an intended recipient of a voice communication and the encoded voice signal sent to the recipient so that it is received, decoded, and provided to the recipient as speech.
Vocoders can employ a variety of encoding techniques and the characteristics of an encoded voice signal depend upon the particular techniques used, such as the algorithms and bit rates employed. Generally, the lower the bit rate used by a vocoder, the fewer number of bits in the resulting encoded signal, and the less bandwidth required for transmitting the encoded signal over a communications network. Thus, the use of lower bit rate vocoders on a communications network can increase network utilization. But while an encoded voice signal produced by a lower bit rate vocoder uses less bandwidth than that produced by of a higher bit rate vocoder, the resulting signal is typically of reduced quality. A lower quality encoded voice signal results in lower quality speech reproduction for the recipient of the voice communication making the voice communication more difficult to understand. Voice communications providers thus face a tradeoff between network efficiency and voice signal quality when selecting a vocoder for use on their networks.
Although the signal quality of first generation low bit rate vocoders was relatively poor, newly developed low bit rate vocoders provide sufficient signal quality to be acceptable for many voice communications, such as person-to-person calls, and low bit rate vocoders have been deployed on some GSM cellular telecommunications networks. But voice quality remains an issue even for these newer low bit rate vocoders, especially in poor signal environments.
One recent attempt to address the tradeoff between signal quality and network efficiency is the development of Adaptable Multiple Rate (AMR) vocoders which have the ability to process voice signals at different bit rates. For example, an AMR vocoder can include a plurality of voice codecs, each rated at a different bit rate. During operation of the AMR vocoder a particular codec having a desired bit rate is used based upon some criteria, such as radio signal strength or interference levels. For example, when signal strength is low a high bit rate codec can be used to produce a high quality encoded voice signal and when signal strength is high a low bit rate codec can be used to produce a low bandwidth encoded voice signal. AMR vocoders thus provide for increased system efficiency by using low bit rate codecs to produce low bandwidth signals for the majority of communications and provide increased voice quality by employing high bit rate codecs when network conditions warrant.
The default behavior of AMR vocoders, however, might not be suitable for certain types of communications. Thus, it would be desirable to provide systems and methods for controlling the characteristics of a voice communication and the associated encoded voice signal generated by a voice communications device based on the intended recipient of the voice communication.